The present invention relates to a cage for the ball bearing which is incorporated for use in a rotational support section of various rotatable machines where low noise, low vibration and low torque are required, specifically in a fan motor for machine tools, general machines and automobiles or in an air conditioner motor, or in a cooling fan motor for various machines and apparatus.
For example, a ball bearing as shown in FIG. 13 is widely used for supporting various rotational portions such as bearings in various rotational machines. This ball bearing comprises an inner ring 2 having an inner ring raceway 1 on its outer peripheral surface and an outer ring 4 having an outer ring raceway 3 on its inner peripheral surface, which are concentric with each other, and a plurality of balls 5 rotatably provided between the inner ring raceway 1 and the outer ring raceway 3, specifically in pockets 7 of a cage 6, respectively.
In the example illustrated, the inner ring raceway 1 and the outer ring raceway 3 are formed in a deep groove type.
The cage 6 of the ball bearing in FIG. 13 is referred to as "corrugated cage " and comprised of a pair of elements 8 which are formed in an annular corrugation by pressing a metal plate member, respectively.
The elements 8 are formed with substantially semicylindrical recess portions 9 to circumferentially define the pockets 7.
The pair of elements 8 are abutted with each other at portions separated from the recess portions 9, and these portions are securely connected with each other by rivets 10, thereby forming the annular cage 6 having pockets 7 arranged in a circumferential direction.
The middle portion on the inner surface of the recess portions 9 is formed in a spherical concave surface in an arcuate cross section having a radius of curvature slightly larger than the radius of curvature of the outer surface of the balls 5. Accordingly, when the pair of elements 8 are abutted to each other, the recess portions 9 are combined to form the pockets 7, respectively.
The cage 11 illustrated in FIG. 14 is referred to as "crown type cage", and comprised of an annular main portion 12 made of synthetic resin etc. where a plurality of resilient pieces 13 are formed on the main portion 12 with a space therebetween, and pockets 7 each including a spherical concave face portion 14 are arranged circumferentially to rotatably support balls 5 (FIG. 13), respectively.
In the cage 11 of the crown type, the pockets 7 are defined by the opposite side faces of a pair of the resilient pieces 13 and the spherical concave ace portion 14 between the opposite side faces, respectively. It will be noted that the resilient pieces 13 and the spherical concave face portions 14 are formed on one axial side face (right face in FIG. 14) of the main portion 12. The term "axial" means substantially left and right directions in FIG. 14.
The radius of curvature of the opposite side faces and concave face portion 14 between the opposite side faces is slightly larger than the radius of curvature of the outer surface of the balls 5.
When assembling the ball bearing, the balls 5 are forcedly inserted, respectively, between the pair of the resilient pieces 13 for the pockets 7 expanding the space between the tip end edges of the pair of the resilient pieces 13. Thus, the balls 5 are nested in the pockets 7 of the cage 11, respectively, and held rotatably between the inner ring raceway 1 and the outer ring raceway 3 (FIG. 13).
During use of the ball bearing with the cage 6 or 11, as the balls 5 rotate, the inner ring 2 and the outer ring 4 are rotated relative to each other. The balls 5 spin around the inner ring 2 while rotating The cage 6 or 11 rotates around the inner ring 2 at the same speed to the spinning speed of the balls 5.
Grease or another lubricant oil is filled in or continuously supplied between the outer peripheral surface of the inner ring 2 and the inner peripheral surface of the outer ring 4 for smooth relative rotation therebetween. Thus vibration and noise, and failure such as seizure are prevented from occurring in the ball bearing.
In some ball bearings, the opposite openings of the space between the outer peripheral surface of the inner ring 2 and the inner peripheral surface of the outer ring 4 are closed with a seal member such as seal plate or shield plate, so that lubricant is prevented from leaking out of the space and any foreign matter such as dust is prevented from entering the space. The ball bearing shown in FIG. 13 has no seal member.
In the case of the ball bearing with the cage 6 or 11, even if the necessary amount of lubricant is filled or supplied, vibrations are caused in the cage 6 or 11, and the noise and vibration, referred to as "cage sound" are sometimes produced in the ball bearing with the cage 6 or 11 incorporated therein.
Such vibration in the cage 6 or 11 is caused due to sliding friction between the balls 5 and the cage 6 or 11 because of large movement amount of the cage 6 or 11 with respect to the balls 5. In order to suppress the cage sound, conventionally, the clearance between the inner surface of the pockets 7 and the rolling contact surface of the balls 5 is minimized, and the movement of the cage 6 or 11 with respect to the balls 5 is minimized to suppress the cage sound.
However, even if the movement amount of the cage 6 or 11 with respect to the balls 5 is minimized, when the operating condition is severe, as in the case of insufficient supply of lubricant, the cage sound may be produced due to the shape of the inner peripheral surface of the pockets 7 of the cage 6 or 11.
Specifically in the case of the conventional cages 6 or 11 as shown in FIGS. 13 and 14, the inner peripheral surface of the pockets 7 is slidable against the rolling contact surface of the balls 5 generally through the whole width, so that the frictional force operating between the inner peripheral surface and the rolling contact surface becomes large. This is detailed referring to FIGS. 15 to 18 hereinafter.
In the case of the conventional structure of FIG. 13, the recess portions 9 in the inner peripheral surface of the pockets 7 are formed with a spherical surface portion 15 throughout its width in the most part thereof, respectively, as shown in FIGS. 15 and 16 by cross hatching. This spherical surface portions 15 function as a hold and guide face having a radius of curvature slightly larger than the radius of curvature of the rolling contact surface of the balls 5 (FIGS. 13 and 16).
In the case of the conventional structure of FIG. 14, the inner peripheral surface of the pockets 7 is formed with a spherical surface portion 15 throughout its whole width, as shown in FIGS. 17 and 18 by cross hatching. This spherical surface portion 15 functions as a hold and guide face having a radius of curvature slightly larger than the radius of curvature of the rolling contact surface of the balls 5.
Due to the spherical surface portion(s) 15 for the hold and guide face formed on the inner peripheral surface of the pockets 7 throughout its width, the friction area between the inner peripheral surface of the pockets 7 and the rolling contact surface of the balls 5 is enlarged, so that the friction vibration produced in the friction contact portion between the cage 6 or 11 and the balls 5 is so large to induce vibration and noise.
In these cases, if the spherical surface portion 15 in the pockets 7 is formed in a single spherical surface throughout its whole width, and if the center O.sub.15 (FIG. 20) of the spherical surface portion 15 of the pockets 7 is displaced from the center O.sub.5 (FIGS. 20 and 21) of the balls 5 in the pockets 7, the lubricant adhering to the rolling contact surface of the balls 5 is scraped off, resulting in large vibration and noise.
This is detailed referring to FIGS. 19 to 21 for the case of the corrugated cage as shown in FIG. 13.
In the conventional cage 6, the radius of curvature R.sub.15 of the spherical surface portions 15 of the pockets 7 formed in a single surface, as shown in FIG. 19, is slightly larger than the radius of curvature R.sub.5 of the balls 5(R.sub.15 &gt;R.sub.5) In addition, the depth D.sub.7, of the pockets 7, which is a half of the inner size of the pockets 7 with respect to the width direction of the cage 6, is slightly smaller than the radius of curvature R.sub.15 of the spherical surface portions 15 as shown in FIG. 20 (exaggerated).
During operation of the ball bearing having such a cage 6 incorporated therein, the rolling contact surface of the balls 5 and the inner surface of the pockets 7 of the cage 6 come into contact with each other, and the balls 5, while rotating, spin around the inner ring 2 at the same speed to the rotation speed of the cage 6.
It should be noted that due to the profile errors in the inner ring raceway 1 and the outer ring raceway 3 (FIG. 13), the relative differences in the balls 5 and/or the inclination of the ball bearing (displacement between the center axis of the inner ring 2 and the center axis of the outer ring) etc., the balls are not completely harmonized with each other in spinning speed, so that slight delay or advance of the balls relative to each other is caused.
As a result, with respect to the balls 5 and the cage 6, the balls 5 sometimes push the cage 6 in the direction of spinning around the inner ring 2 and the cage 6 sometimes pushes the balls 5. In each case, the rolling contact surface of the balls 5 comes in contact with the spherical surface portions 15 of the inner surface of the pockets 7. Specifically, the radius of curvature R.sub.15 of the spherical surface portions 15 is larger than the radius of curvature R.sub.5 of the balls 5, the cage 6 is radially displaced by a distance equal to the clearance based on the differences between the radius of the curvature R.sub.15 and the radius of curvature R.sub.5 as shown in FIG. 21. In this condition, the rolling contact surface of the balls 5 comes into sliding contact with the spherical surface portions 15 of the pockets 7.
Specifically in this condition, as shown in FIGS. 20 and 21, the spherical surface portions 15 of the pockets 7 and the rolling contact surface of the balls 5 come into sliding contact with each other on either side in the width direction (up and down directions in FIG. 20, left and right directions in FIG. 21) of the cage 6, specifically at two points P.sub.1 and P.sub.2 which are separated from the circumferentially central portion of the pockets 7 toward a circumferential end.
When the center O.sub.7 of the pockets 7 of the cage 6 is displaced radially inward from the center O.sub.5 of the balls 5 as shown in FIG. 21 due to the clearance based on the difference between the radius of curvature R.sub.15 and the radius of curvature R.sub.5, a portion in the rolling contact surface of the balls 5 closer to the radially outer periphery of the cage 6 comes into sliding contact with a portion of the spherical surface portions 15 of the pockets 7 closer to the radially outer periphery of the cage 6. The lubricant such as grease and oil adhering to the rolling contact surface of the balls 5 for lubrication of the ball bearing is scraped off by the spherical surface portions 15, so that this lubricant would not enter the pockets 7 and be pushed out of the pockets 7.
On the other side in the circumferential direction of the cage 6, a portion of the rolling contact surface of the balls 5 closer to the radially inner periphery of the cage 6 comes into sliding contact with a portion of the spherical surface portions 15 of the pockets 7 closer to the radially inner periphery of the cage 6, which would also cause shortage in feeding of the lubricant.
As a result, the sliding friction coefficiency at the sliding contact portions between the spherical surface portions 15 of the pockets 7 in the cage 6 and the rolling contact surface of the balls 5 increases, and the friction torque of the ball bearing with the cage 6 incorporated therein varies or increases, and the friction sound of the balls occurs in operation, sometimes outstandingly.